Method of manufacturing frame grids for use in electron valves



United States Patent 3, 9 6 Claims. (Cl. 29-155.5)

The invention relates to a method of manufacturing frame grids for use in electron discharge tubes.

Such a frame grid comprises a frame of molybdenum or a FeNi-Co alloy (Fernico), on which metal wire is wound in one direction; Hitherto theturns were applied to the frame by means of notches, in which the wire was guided during the winding process, after which the wire was pressed tight. However, this method is quite unsuitable for the manufacture of frame grids with extremely thin grid wires (for example of a diameter of to 10p.) and a very small pitch (for example SO/L for single side windings and 100 for double-side windings).

The last-mentioned type of frame grids are employed for example in indicator tubes comprising ten cathodes shaped in the form of the digits 0 to 9, an anode and one or more of these frame grids arrangedv between groups of these digital cathodes or between each pair of these cathodes. The digital cathodes can be caused to luminesce by the application of a voltage. As aematter of course, the frame grids used in this case must have a very high transparency.

These frame grids may also be employed in amplifying tubes with a view to -a satisfactory i,,-V characteristic curve of such a tube, the pitch of the winding must be at a minimum.

In the manufacture of such frame grids having a grid wire of 5 to 10 and a pitch of 50 various efforts have been made to fix the wire to the frame. It has been proposed to weld a metal strip across the turns, where they are in contact with the frame Welding was carried out on either side adjacent the turns, since welding across the winding readily gave rise to breakage or disengagement of the wire. With this welding method, however, the wire remained loose, so that it could readily shift.

. It has also been proposed to affix the turns by means of an enamel layer, applied by means of a suspension. This did not provide a satisfactory solution either, since the suspension is likely to penetrate between the turns.

The fastening of the wire should not require an excessively high temperature; the conventional materials for the frame, molybdenum or iron-nickel-cobalt alloys have a considerably higher thermal expansion coefiicient than the wire material, tungsten. After cooling the wire is insufficiently taut, since the elasticity limit has been surpassed.

There is known a method of interconnecting metal parts having a melting point exceeding 1400 C., in which at least one of the surfaces of the parts is provided, at the area of their junction, with a thin phosphorus-containing nickeland/or cobalt layer having a phosphorus content of less than and in which the parts are heated, while being in contact with each other, in a protective atmosphere at a temperature between 800 C. and 1400 C. for such a long time that substantially the whole quantity of phosphorus has disappeared from the layer, so that the melting point of the metal layer rises considerably.

This method is employed for fastening grid wires to a frame, the prolonged heating for reducing the phosphorus content of the layer being, however, omitted.

is too high for the present purpose.

3,246,387 Patented Apr. 19, T966 Moreover, this known method is not suitablewithout the need for further measures. In the known currentless nickel-plating process it is not possible to obtain a phosphorus-containing layer of adequately lowmelting point. This melting point is usually 1100" C. to' 1200 C, which A phosphorus-containing nickel layer of adequately low melting point could, it is true be obtained by electro-deposition, but for the small parts concerned hereinthis method is particularly circuitous and requires special tools.

a In accordance with the invention 'the frame is coated with a phosphorus-containing nickel. layer by means of an electroless nickel-plating bath consisting of an aqueous solution containing nickel ions, hypophosphite ions and -a compound forming a complex with nickel ions, in which solution the mol percent ratio between hypophosphite and nickel is at least 3, and the mol percent ratio between the compound forming complexes with the nickel ions and the nickel is at least 2, said bath having a pH value lying between 4 and '7, after which the grid wire is wound onthe frame and. the assembly is heated at a temperature lying between 700 C. and 800 "C;

From experiments leading to the invention it has been found that owing to the presence .of nickel in the complex state in an acid solution the deposited. nickel has a considerably higher phosphorus content than nickelldeposited from a bath without such a complexproducer. Apparently the velocity of reduction to metallic nickel is diminished in this way, while the dissociation ofhypophosphite, while phosphorus is formed, is only slightly affected or is not affected at all. g

The quantity of the complex produced to be added to the bath must be chosen so that about 50 to of the nickel ions in the bath are bound in 'a complex manner. This consequently depends on the dissociation constant of the nickel complex to be obtained. To this end the mol percent ratio between the compound forming complexes with the nickel and the nickel must at any rate be at least 2. a

In the following table the content of phosphorus in the deposited nickel is indicatedin dependence uponthe quantity of citric acid added as a complex producer to an electroless nickel-plating bath.

Table Phosphorus Citric acid, percentage in N1++ mol. percent mol. percent the deposited nickel A different complex producer is, for example, hydroxyacetic acid. Owing to the high phosphorus content of the nickel deposited by means of a bath used in accordance with the invention the melting point amounts from 700 C. to 800 C.

When the grid wire is then wound on the frame thus nickel-plated, and the assembly is heated at a temperature between 700 C. and 800 C., the nickel coating serves at the same time as a buffer layer for compensating the difference between the expansion coeflicient of the frame and the grid wire; during heating there is no risk of the wire being stretched in excess of the elasticity limit, since it is drawn into the molten surface layer, when the temperature is raised. After cooling the wire is taut and an excellent adhesion to the frame is obtained. The heating time need be only short. It was found that in spite of the high phosphorus content of the nickel layer the lifetime and the quality of the electron discharge tube were not adversely affected.

In a preferred method embodying the invention the complex producer in the electroless nickel-plating bath is formed by an acid neutralizing complex former on the basis of an amine. Examples of such complex formers are ethylene diamine, ammonium ions or amino-acetic acid. By adding these acid neutralising complex formers the pH remains practically constant; without the buffer effect this value would drop gradually owing to the reaction:

so that the velocity of deposition gradually decreases. The separate addition of a buffer is in this case required.

By adding to the nickel-plating bath an acid neutralising complex former for nickel ions, the following reaction may occur instead of the aforesaid reaction, for example with the addition of ethylene diamine:

Nil, H2P0, fur ow-Griffin, as a result of which the pH of the solution remains substantially constant.

An example of a bath which may be used within the scope of the invention, is formed by a solution containing per litre 16 gms. of NiCl .6H O, 80 gms. of amino-acetic acid, 24 gms. of NaH PO .H O and 6.8 gms. of NaOH. The pH value of this solution is 5.5 and is still 5.5 when the bath is exhausted for 95% after use.

It should be noted that a few compounds which may serve as complex producers have been proposed as additions to electroless nickel-plating baths. There is known a bath containing an aqueous solution of nickel ions, hypophosphite ions and an aliphatic aor B-amino-carboxylic acid and/ or a salt thereof, in which the mol percent ratio between nickel and hypophosphite lies between 0.25 and 1.6 and the mol percent ratio between amino-carboxylic acid and nickel lies between 0.5 and 6 and the pH value of the solution lies between 4.5 and 9.0. The addition of the amino-carboxylic acid in this known method is intended to reduce the production of black deposits owing to occlusions of insoluble nickel phosphite. The recognition that by the addition of a complex producer to a nickel-plating bath under the aforesaid conditions a nickel layer having a high phosphorus content and a low melting point is obtained which permits of manufacturing frame grids for use in election discharge tubes of excellent quality, does not prevail in the known method.

The nickel-plating should occur at a temperature of C., in order to attain an adequate deposition velocity for the nickel.

When a nickel layer is simultaneously applied to a large number of frames, it is advisable, in order to obtain a uniform coating, to carry out the nickel-plating process in a rotating drum. The thickness of the nickel layer to be applied may amount from 2 to 5 What is claimed is:

1. A method of manufacturing a grid for an electron discharge tube, said grid comprising a frame and a metal Wire wound in one direction on said frame, the method comprising the steps, placing the frame in an electroless nickel-plating bath containing an aqueous solution of a soluble nickel salt, a hypophosphite, and a compound which forms a complex with nickel ions, the said nickel salt and hypophosphite being in a mol percent ratio of at least 3, said nickel complex forming compound and said nickel salt being in a mol percent ratio of at least 2, said solution having a pH of between 4 and 7, to form a nickel coating with a phosphorus content on the frame at which the coating melts at a temperature of about 700 to 800 C., winding a wire about the so-coated frame, and heating the so-coated frame and wire to a temperature of about 700 to 800 C. to melt the coating and secure the wire on the frame.

2. A method as claimed in claim 1 in which the nickel complex forming compound is an acid neutralizing complex former.

3. A method as claimed in claim 2 in which the nickel complex forming compound is ethylene diamine.

4. A method as claimed in claim 2 in which the nickel complex forming compound is amino-acetic acid.

5. A method as claimed in claim 1 in which the nickel complex forming compound is citric acid.

6. A method as claimed in claim 1 in which the nickel complex forming compound is hydroxyacetic acid.

References Cited by the Examiner UNITED STATES PATENTS 2,610,387 9/1952 Borland 29155.5 2,658,841 11/1953 Gutzeit et al 106-1 X 2,961,759 11/1960 Weissfloch 29-4723 2,962,811 12/1960 Herbert 20-494 WHITMORE A. WILTZ, Primary Examiner.

RICHARD H. EANES, Examiner. 

1. A METHOD OF MANUFACTURING A GRID FRO AN ELECTRON DISCHARGE TUBE, SAID GRID COMPRISING A FRAME AND A METAL WIRE WOUND IN ONE DIRECTON ON SAID FRAME, THE METHOD COMPRISIG THE STEPS, PLACING THE FRAME IN AN ELECTROLESS NICKEL-PLATING BATH CONTAINING AN AQUEOUS SOLUTION OF A SOULBLE NICKEL SALT, A HYPOPHOSPHITE, AND A COMPOUND WHICH FORMS A COMPLEX WITH NICKEL IONS, THE SAID NICKEL SALT AND HYPOPHOSPHITE BEING IN A MOL PERCENT RATIO OF AT LEAST 3 SAID NICKEL COMPLEX FORMING COMPOUND AND SAID NICKEL SALT BEING IN A MOL PERCENT RATION OF AT LEAST 2, SAID SOLUTION HAVING A PH OF BETWEEN 4 AND 7, TO FORM A NICKEL COATING WITH A PHOSPHORUS CONTENT ON THE FRAME AT WHICH THE COATING MELTS AT A TEMPERATURE OF ABOUT 700* TO 800*C., WINDING A WIRE ABOUT THE SO-COATED FRAME, AND HEATING THE SO-COATED FRAME AND WIRE TO A TERMPERATURE OF ABOUT 700* TO 800*C. TO MELT THE COATING AND SECURE THE WIRE ON THE FRAME. 